Electroluminescent devices



Jan. 26, 1960 s. YANDo ELEcTRoLuMINEscENT DEVICES 2 Sheets-Sheet 1 FiledMarch 19, 1959 THIRD on #L m MR ww SW/ M w A .HK Mm MW/ 6 0 R m mm 4ww/@ mw. M

FIRST DIFFERFNT- SECOND /FFERFNT IAT/0Nl NETWORK F/RS T HALF WAI/EREC'T/F/ER WBRATUR /AT/ON NETWORK .sm/VAL l SA W TOOTH GENERATOR FIRSTPULSE TRA/N JECOA/ PULSE TRA/N INVENTOR STEPHEN )f4/"D0 ATTORNEY United`States Patent M ELEcTRoLUix/irNEscENT DEVICES Stephen Yando, Huntington,N.Y., assignor to Sylvania Electric Products Inc., a corporation ofDelaware Application March 19, 1959, Serial No. 800,434

11 Claims. (Cl.- 315-?5'5) My invention is directed towardelectroluminescent devices.

(or scan) an electroluminescent layer.

As explained in more detail in this application, first and secondcontacts, positioned opposite each other, are secured to oppositesurfaces of a crystalline piezoelectric strip adjacent one end thereof.An electroluminescent layer is placed in intimate engagement with onesurface of the strip intermediate one of the contacts and the other endof the strip. A voltage pulse, applied between the contacts, produces,in the portion of the strip subtended by the contacts, a mechanicalstrain proportional to the amplitude of the pulse. The changing strainproduces a disturbance, in the form of an elastic wave accompanied by anelectric eld, which propagates along the strip from the contacts towardthe other end of the strip. As the elastic wave propagates along thestrip, the accompanying electric eld products a spot of light in theelectroluminescent layer which moves in synchronism with the wave.

In the above described invention, the period of time (or scanninginterval) required for the spot of light to traverse theelectroluminescent layer is determined both by the velocity ofpropagation of the elastic wave within the strip, and the length of theelectroluminescent layer. For any selected type of strip, this velocityisa constant, and the scanning interval can only be varied by increasingor decreasing the length of the strip.

I have succeeded in eliminating the interdependence of Y 2,922,923Patented Jan. 26, 1960 ICC 2 strip (i.e. the surface of theV stripremote from the electroluminescent layer).

First and second pulse trains are applied between the first and secondcontact pair and the third and fourth contact pair respectively. Eachpulse in each of these trains produces, in the corresponding rst orsecond section of the strip, a mechanical strain proportional to theamplitude of the pulse. As this strain changes, la disturbance in theform of an elastic wave accompanied by an electric eld, 'propagatesalong the strip from the appropriate section towards the other end ofthe strip where it is absorbed substantially without reflection.

More particularly, each pulse in the first pulse train produces a firstelastic wave, accompanied by a first electric field, which propagatesfrom the first section toward the second section of the strip.Similarly, each pulse in the second pulse train produces a secondelastic wave, accompanied by a second electric field, which propagatesfromthe second section towardthe first section.

The intensity of each electric eld is proportional to thetime rate ofchange of the strain which produced it; stated'differently, theintensity of each electric field is proportional to the first timederivative of the pulse which produced the lield.

When any rst wave intersects any second wave, the corresponding electricfields are additive at the part of intersection.

A third pulse train is applied between the front and back electrodes.Each pulse in the third train produces a third electric eld which isperpendicular to both electrodes and which is uniform Vthroughout theentire electroluminescent layer. At any point of Wave intersection, thelirst, second and third fields are additive and produce a spot of lighton the electroluminescent layer at a position corresponding to thispoint yof intersection. The amount of light emittedy from this spot isdetermined by the total field intensity and increases monotonically thescanning interval and the velocity of propagation of an elastic wave inan electroluminescent device of the character indicated. Moreparticularly, I am able to vary the scanning interval while maintaininga fixed length of piezoelectric strip and, conversely, am able to varythe length of the strip while maintaining a iixed scanning interval.

In accordance with the principles of my invention, first and secondcontacts are respectively secured to opposite surfaces of a strip ofcrystalline, piezoelectric material adjacent one en'd thereof and thussubtend a first section of the strip. Further, third and fourth contactsare respectively secured to the front and rear surfaces of the stripadjacent the other end of the strip and thus subtend a second section ofthe strip. The ends of the strip are terminated in such manner as toabsorb, substantially without reflection, any incident elastic wavesupplied thereto fromsaid strip.

An electroluminescent layer is placed in intimate engagement with thefront surface of the strip in a position intermediate the appropriatecontacts. A transparent electrode (the front electrode) is applied overthe exposed surface of this layer. Further, another electrode Y -(theback electrode) is applied to the rear surface ofthe therewith.

The position of the spot of light depends upon the relative timing ofthe pulses in the three pulse trains. Hence, by continuously varying therelative timing of these pulses, the spot of light will scan the stripat a velocity dependent upon the rate of timing variation. Further, thelight intensity of this spot can be modulated by appropriately varyingthe pulse amplitude.

Illustrative embodiments of my invention will now be described withreference .to the accompanying drawings wherein- Fig. 1 is an isometricview of one embodiment of my invention;

Fig. 2`is a block diagram of an electronic system wherein the. relativetiming and amplitudes ofthe rst, second and third pulse trains can bevaried as required for the device of Fig. l; and l Figs. y5--7 show thewaveforms of signals utilized in the system of Fig. 2.

Referring now to Fig. 1, there is shown a thin strip or ribbon 10 ofpiezoelectric material; in this example the material is a polarizedceramic strip composed of a sinteredlead titanate-lead zirconatemixture. First and second contacts 12 and S14 which extend transverselyto the long axis of the strip are secured to opposite surfaces of thestrip adjacent the left end thereof; these electrodes are positionedopposite each other and subtend a first section 16 of the strip.Similarly, third and fourth transverse contacts 18 and 20 are secured toopposite surfaces of the strip adjacent the right end thereof andsubtend a second region 22 of the strip.

An electroluminescent layer 24 is placed in intimate contact with onesurface of strip 10 intermediate the ends .thereof and spaced apart fromthe contacts 12 and 18.

A transparent or front electrodefZ covers the exposed surface of layer24. A second or back electrode 28 covers the same area as frontelectrode 26, but is applied to the surface of strip remote fromelectroluminescent layer 24.

Each end of the strip, as explained in more detail in the abovementioned copending application Serial No. 776,980, is terminated insuch manner as to absorb, substantially without reflection, any incidentelastic wave propagating in said strip. This is accomplishedV by coatingthe ends and immediately adjacent portions of strip 10 with a material,such as lead, to provide terminations and 3'2.

First and second pulse trains are applied between contacts 18 and 20 andcontacts 12` and 14, respectively. Each pulse in each train establishesa corresponding electric field within an appropriate one of sections 16and 22. The electric field intensity is proportional to theinstantaneous value of the appropriate voltage pulse.

Due to the piezoelectric characteristics of strip 10, each electricfield produces, in the corresponding section 16 or Z2, a mechanicalstrain proportional to the instantaneous field intensity. Hence, thisstrain is proportional to the instantaneous value of the pulse. Thestrain produces a disturbance which is proportional to the time rate ofchange of the strain and, consequently, is also proportional to thefirst time derivative of the pulse. This disturbance propagates alongthe strip in the form of oppositely directed elastic waves travellingtoward the right hand and left hand respectively of strip 10.

More particularly, the first pulse produces a first elastic wave whichtravels from section 22 toward the left hand end of the strip. (Thefirst pulse also produces an oppositely directed wave which is absorbedalmost immediately in termination 32 and has no influence upon theoperation of my device.) The second pulse produces a second elastic wavewhich travels from section 16 toward the right hand end of the strip.(The second pulse also produces an oppositely directed wave which isabsorbed in termination 30.)

Each of the first and second waves, due to the piezoelectric eiect, isaccompanied by an electric field, the intensity of which is proportionalto the first time derivative of the appropriate pulse. The intensitiesof both fields are additive at the point of intersection of the firstand second waves.

A third pulse train is applied between the front and back electrodes 26and 28 respectively. Each pulse in the third train is generated at suchtiming with respect to the pulses in the first and second train as toestablish a third uniform electric field within the entireelectroluminescent layer 24 at the time at which the desiredintersection of the first and second elastic waves ensues. Since, withthis timing, the intensities of the three electric fields are additiveat the point of intersection, a spot of light is produced inv theelectroluminescent layer at a position corresponding to this point. Theamount of light produced increases monotonically with increasing totalfield intensity.

The intersecting waves, in the absence of the third pulse train, tend toproduce a spot of light in the electroluminescent layer at a positioncorresponding to the point of intersection. However, the non-linearvoltagebrightness characteristics are such that suitable adjustment ofpulse amplitudes can reduce any spurious or background lighting toinsignificant levels. For example,

when the pulses in the first and second trains each have an amplitude ofV volts, and the pulses in the third train have a value ranging betweenO-V volts, spurious lighting effects are substantially eliminated.

The intersection of any first elastic wave with any second elastic wavecan be viewed as establishing a light aperture at a selected position onthe electroluminescent layer 24; light will be produced in this apertureonly when a pulse in the third train is applied with proper timingbetween the front. and back electrodes.

When Vthe first and second voltage pulses arrive in time synchronism atthe corresponding Contact pairs, the aperture will be positioned at themidpoint between the contact pairs. When the first pulse leads thesecond pulse, the aperture will be displaced to the right of themidpoint; when the second pulse leads the first pulse, the aperture willbe displaced to the left of the midpoint.

More particularly, the time interval required for the elastic wave totraverse that segment of strip 10 in contact with the electroluminescentlayer 24 is normally some constant K. When substantially identical firstand second pulses are supplied to the corresponding contact pairs at thesame time to, the corresponding first and second waves will intersect atthe midpoint of layer Z4 at time to-l-K/Z. Hence, by supplying a pulsein the third train between the front and back electrodes at time t0+K/2, light will be produced at this midpoint.

When the second pulse is supplied at time to, while the first pulse issupplied at time tO-l-K, the waves will intersect at time to-l-K, andtheY aperture will be immediately adjacent contact 12. The pulse in thethird train must be supplied at time to-l-K to illuminate the aperturethus formed.

On the other hand, when the Vsecond pulse is suppliedl at time to, whilethe first pulse is supplied at time t0,-K, the waves will intersect attime to, and the aperture will be immediately adjacent contact 18. IInthis case, the pulse in the third train must be supplied at time t0 toproduce light in this aperture.

In this manner, the spot of light can be produced in any desiredhorizontal position along the electroluminescent layer. Further, thespot can be moved in successive positions from the extreme left hand tothe extreme right hand edges of the electroluminescent layer 24, thusproducing the desired scanning action.

The scanning action can be carried out in the following manner. A firstpulse train containing x separate first pulses (where x is the number ofdifferent positions assumed by the spot of light in traversing thelength of the electroluminescent layer) is applied between contacts 12and 14. A second pulse train containing x separate second pulses isapplied between contacts 18 and 20. A third pulse train containing xseparate third pulses is applied between the front and back electrodes24 and 26.

The time relationship between each Nth first, second and third pulses(where N is any integer from l to x) is adjusted as follows. The Nthfirst pulse is produced at time 2a (where a is smoothly varied from 0when N is equal to l to K when N is equal to x). The Nth second pulse isproduced at time K (i.e. the time separation between the Nth second andfirst pulses is K-Za). The Nth third pulse is produced at time K-l-a(i.e. the time separation between the Nth second and Nth third pulses is-a).

In particular, the scanning operation is initiated when the first pulsein the first train leads the first pulse in the second train by K andthe first pulse in the third train is in time coincidence with the firstpulse in the second train. The scanning operation is completed when thexth pulse in the first train lags the xth pulse in the second train by Kand the xth pulse in the third train is in time coincidence with the xthpulse in the first train. The resulting relationships between the first,second and third pulse trains are shown graphically in Fig. 7.

It is desired that the electroluminescent layer be excited by sharp,spike-like pulses. Due to the differentiating action of the strip 10,the pulses in both the first and second trains must have the sawtoothwaveform shown to provide this type of excitation.

A block diagram of circuitry for accomplishing the scanning operation isshown in Fig. 2. (The circuitry designated by each block in this diagramis conventional and will not be shown here.) Y

The circuit of Fig. 2 is actuated by an input signal constituted by xseparate, equidistantly spaced timing or triger pulses... Thetimespacingbetween adjacent trigger :pulsesY is K or in other words, the.recurrencefrequenc'y of the trigger pulses is l/K. f 1

I The trigger pulses are supplied through a frequency .divider 100 tothe input of a saw tooth generator 102. 'Divider 100 produces one sharpdivider pulse for every 'group of x trigger pulses supplied to thedivider input. More particularly, the divider produces an output pulsettor each incoming (mx) trigger pulse, where m is any integer and x hasbeen defined previously. Each divider 'pulse actuates the generator 102which thereupon yields an output voltage having a sawtooth waveform.This voltage increases positively from O, the period of the sawtoothbeing xK.

The trigger pulses are also supplied to a rst multibrator 104. Theoutputof multivibrator 104 is coupled to the input of a second multivibrator106. These two multivibrators 104 and 106 lhave variable but equalperiods of a seconds, where al varies from essentially 0 when the firsttrigger pulse arrives, to- K when the xth trigger pulse is received. Thelength of both equal periods lis determined by a controlvoltage suppliedfrom the output of sawtooth generator 102- to the'control inputs 108:and 110 of multivibrators 104 and 106 respectively.

The output signal yielded by the second multivibrator 7106 passessuccessively through a rst differentiation network 112 and a rst halfwave rectilier 114 to the input of pentode tube 116. The output circuitof tube 116 is coupled between contacts 18 and 20 of strip 10 of Fig. 1.The resultant signals appearing between terminal 202 and ground and thussupplied to strip 10 from tube 116 form the rst pulse train of xseparate pulses having a sawtooth waveform. y

'Ihe output of the first multivibrator 104 is also coupled to the inputof a third multivibrator 118. (Multivibrator 118 has a fixed periodequal to the interval K.) The output signalryielded by the thirdmultivibrator 118 passes successively through a second diierentiationnetwork 120 to the input of pentode tube 122. The output circuit of tube122 is coupled between the front and back` electrodes 24 and 26 of thestrip 10 of Fig. 1. The resultant signals appearing between terminal 204and ground and thus supplied to these front and back electrodes fromtube 122 is the third pulse train of x separate pulses having a spikeWaveform. The amplitudes of the pulses in the third train are increasedor decreased with the amplitude variations of a modulation signalsupplied to the input of tube 122.

The trigger pulses are also supplied to the input of a fourthmultivibrator 124. (Multivibrator 124 has a fixed period equal to theinterval K.) The output signal yielded by multivibrator 124 passessuccessively through a third ydifferentiation network 126 and a secondhalf wave rectifier 128 to the input of pentode tube 130.` The outputcircuit of tube 130 is coupled between contacts `12 and 14 of strip 10of Fig. 1. The resultant signals appear- 'ingbetween terminal 20,0 andground and thus supplied `to strip 10 from tube 130 form the secondpulse train of x separate pulses having a sawtooth waveform.

The operation of the system of Fig. 2 will now be described withreference to the waveforms shown in Figs. 3a-3e. Thesewaveforms show aportion of the pulse sequence.

The triggerv pulses (Fig. 3a) are supplied through frequency divider100to the input of the sawtooth generator 102 which produces van outputvoltage having a sawtooth waveform (Fig. 3f) in the manner previouslydescribed.

Further the trigger pulses are supplied to the input of the firstmultivibrator 104. Upon the'arrival of each trigger pulse, the firstmultivibrator produces a rectangular shaped pulse (Fig. 3b) having aperiod a which increases from essentially 0 to K in accordance with Vthechanging Ysawtooth voltage developed by generator 102 and is supplied asa control input to multivibrators 104 and 106. Upon the termination of aYirst'period of a, the second multivibrator produces another rectangularshaped pulse`(Fig. 3c) having the same variable period a. Therectangular shaped pulses appearing at the output of the secondmultivibrator, ,as can be seen from Fig. 4, aredtferentiated in network112, toproduce alternatively positive and negative pulses (Figi. 4).These positive and negative going pulses` are supplied to the rst halfwave rectier 114 which permits only the positive pulses to passtherethrough (Fig. 4). These positive pulses then pass through tube 116and appear across contacts 18 and 20 of strip 10 of Fig. 1 as the irstpulse train of x separate, equidistantly spaced pulses (Fig. 4). (Thetwo contacts 18 and 20 together with the section 22 of strip 10constitute a capacitor. The combination of this capacitor and theresistor in the plate circuit of tube 116 acts upon the pulses passingthrough tube 116 to change their waveform from a spiketo a sawtooth. Aspreviously indicated, this waveform conversion is required` because ofthe differentiating yaction ofthe rstrip 10.)

The Vrectangular shaped' pulsefromk the first multivibrator 104 is Yalsosupplied to the `input of the third multivibrator 118. As shown in bothFigs. 3b and 3e and in Fig. 6b, upon ,the ,termination'of each pulse forthe. first multivibrator 104, the third multivibrator 118 produces arectangular shaped pulse having a fixed period K. This fixed periodpulse is differentiated in the second differentiation network to producealternative positive and negative pulses (Fig. 6c), and the positivepulses pass through' tube 122 to produce `the `third pulse train of xseparate pulses having a spike waveform (Fig. 6d).

As shown in Fig. 5, the incoming trigger pulses are also supplied to theinput of the fourth multivibrator 124. Upon the arrival of each triggerpulse (Fig. 5a) the fourth multivibrator produces arectangular shapedpulse having a fixed period K (Fig. 5b). These pulses are thendifferentiated in the third differentiation network 126 to producealternative negative andY positive pulses (Fig. 5c). The positive pulsespass Athrough the second half wave rectifier 128 (Fig. 5d) to the inputof tube 130. In the same manner as previously described, these pulsesare converted to the second pulse train of y different pulses having asawtooth waveform (Fig. 5e).

In this manner, a spot of'light'is caused to traverse theelectroluminescent layer, the intensity of the light spot and thevelocity of travel of the spot being determined by the amplitudesandrelative timing of pulses in the pulse trains. f It will be apparentthat since contacts' 14 and 20 and the back electrode are grounded,these contacts and electrode are electrically .interconnected and can bereplaced by a single common electrode.

1. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contactssecured toopposite surfaces of said strip adjacent the 'other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of th'e strip and spaced apart from saidcontacts; a rst transparent electrode covering the exposed surface ofsaid layer; and a second electrode covering the surface of said stripremote from said layer and spaced apart from the appropriate contacts. fi

2. An electroluminescent device comprising a strip of piezoelectricmaterial; rstand` second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third andfourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer'placed in intimate engagement with one of saidsurfaces intermediate the ends of'the strip and spaced apart from saidcontacts; a first transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced apart from the appropriate contacts, andiirst and second'terminations axed to corresponding ends of said strip,said terminations absorbing substantially without reflection anyincident elastic wave supplied thereto from said strip. j

3. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second Vcontacts secured to opposite surfaces ofsaid strip adjacent one end thereof; third and fourth contacts securedto opposite surfaces of said strip adjacent the other end thereof;an'electroluminescent layer placed in intimate engagement'with one ofsaid surfaces intermediate the ends of the strip and spaced apart fromsaid contacts; a first transparent electrode covering the exposedsurface of said layer; a second electrode covering the surface of saidstrip remote `from said layer and spaced apart from the appropriatecontacts; first and second terminations afixed vto corresponding ends ofsaid strip, said terminations absorbing substantially without reflectionany incident elastic wave supplied thereto from said strip; means toapply a first pulse train between said first and second contacts; meansto apply a second pulse train between Isaid third and fourth contacts,and means-to apply a third p ulse vtrain between said first and secondelectrodes.

4. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidcontacts; a first transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced apart from the -appropriate contacts; firstand second terminations afiixed to corresponding ends of said strip,said terminations absorbing substantially without reflection anyincident elastic wave supplied thereto from said strip; means to apply afirst pulse train between said first and second contacts; means to apply-a second pulse train between said third and fourth contacts, and meansto apply a third pulse train between said first and second electrodes,the pulses .in said first and second trains having a sawtooth waveform,the pulses in said third train having a spike waveform.

5. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidcontacts; a first transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced apart from the appropriate contacts; firstand second terminations affixed to corresponding ends of said strip,said terminations absorbing substantially without reflection anyincident elastic wave supplied thereto from said strip; means to apply afirst pulse train between said first and second contacts; means to applya second pulsev train between said third and fourth contacts; means toapply a third pulse train between said first and second electrodes, thepulses in said first and second trains having a sawtooth waveform, thepulses in said third train having a spike waveform; the pulses in saidfirst and second train having a constant peak amplitude, the pulses insaid third train being amplitude modulated.

6. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from` saidcontacts; a first ytransp-arent electrode covering the exposed surfaceof said layer; a second electrode covering the surface of said stripremote from said layer and spaced apart from the appropriate con tacts;first and second terminations affixed to corresponding'ends of saidstrip, said terminations absorbing sub stantially without reflection anyincident elastic wave supplied thereto from said strip; means to apply afirst pulse train between said first and second contacts; means to applya second pulse train between said third and fourth contacts, means toapply a third pulse train between said frrst and second electrodes; andmeans to vary the relative timing of corresponding pulses in each ofsaid first, second and third trains.

7. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidlcontacts; a first transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced lapart from the appropriate contacts; firstand second terminations absorbing substantially without reection anyincident elastic wave supplied thereto from said strip; means to apply afirst pulse between said first and second contacts; means to -apply asecond pulse between said third and fourth contacts; and means to applya third pulse between said first and second electrodes.

8, A device as set forth in claim 7 further including means to vary therelative timing of said first, second and third pulses.

9. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidcontacts; a first transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced apart from the appropriate contacts; firstand second terminations affixed to corresponding ends of said strip,said terminations absorbing substantially without reflection anyincident elastic wave supplied thereto from said strip; means to apply afirst pulse between said first and second contacts to produce a firstelastic wave which, accompanied by a first electric field, propagatesalong said strip toward said other end; means to apply a second pulsebetween said third and fourth contacts to produce a second elastic wavewhich, accompanied by a second electric field, propagates along saidstrip toward said one end, said first and second waves intersecting andestablishing a light aperture at a position along said strip dependingupon the relative timing of said first and second pulses; and means toapply a third pulse between said first and second electrodes at suchtiming with respect to said first and second pulses as to illuminatesaid aperture.

10. An electroluminescent device comprising a strip of piezoelectricmaterial; first and second contacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidcontacts; a first transparent electrode covering the exposed surface ofsaid layer; and a second electrode covering the surface of said stripremote from said layer and spaced apart from the appropriate contacts,said second and fourth contacts and said sec- 9 ond electrode beingelectrically' interconnected to form a common electrode.

11. An'electroluminescent device comprising a strip of piezoelectricmaterial; rst and secondcontacts secured to opposite surfaces of saidstrip adjacent one end thereof; third and fourth contacts secured toopposite surfaces of said strip adjacent the other end thereof; anelectroluminescent layer placed in intimate engagement with one of saidsurfaces intermediate the ends of the strip and spaced apart from saidcontacts; a rst transparent electrode covering the exposed surface ofsaid layer; a second electrode covering the surface of said strip remotefrom said layer and spaced apart from the appropriate contacts, saidsecond and 'fourth contacts and said second electrode being electricallyinterconnected to forma common electrode; rst and second terminationsaxed to corresponding ends of said strip, said terminations absorbingsubstantially without reflection any incident elastic wave suppliedthereto from said strip; means to apply a irst pulse between said rstcontact and said common electrode; means to apply a second pulse betweensaid third contact and 1 said common electrode; and means to apply athird pulse between said first and common electrodes.

No references cited.

